Skin Diseases That Cause Dark Spots. 1  Melasma: Itâs one of the commonest causes of grayish patches on the face. It mostly affects the forehead, cheeks, or the area between your mouth and nose. 2  Riehlâs Melanosis: It causes grayish or brownish patches on your face resulting from hyper-pigmentation.
In biology, tissue is a cellular organizational level intermediate between cells and a complete organ.A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.The study of tissue is known as histology or, in connection with disease, histopathology.unctions of epithelial tissue: 1  the cells of the body surface form the outer layer of skin. 2  inside the body, epithelial cells form the lining of the mouth & alimentary canal & protect these organs. 3  epithelial tissues help in absorption of water & nutrients.
In biology, tissue is a cellular organizational level intermediate between cells and a complete organ. A tissue is an ensemble of similar cells from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.The study of tissue is known as histology or, in connection with disease, histopathology.lant tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and the vascular tissue. 1  Epidermis-Cells forming the outer surface of the leaves and of the young plant body. 2  Vascular tissue-The primary components of vascular tissue are the xylem and phloem.